Regulated DC Power Supply

DC Power Supply: DC power supply is a traditional electronic device which takes AC power from AC mains and converts it into DC power to operate various electronic DC appliances. In electronic laboratory the DC power supply is a common instrumental device which used as DC voltage source. Another DC sources like dynamo or battery is more costly than DC power supply. DC power supply also has long-lasting and voltage adjustable facility which are suitable for experimental work in laboratory. In this tutorial we will know how to create a regulated DC power supply.

 

Regulated DC 5V supply

Objectives:

(i) To know use of rectifier circuit
(ii) To know use of step-down transformer.
(iii) To know use of filter circuit.
(iv) To know use of voltage regulator ICs.
(v) After all to learn the creation and use of a simple DC voltage source.

Schematic Diagram: A schematic diagram of regulated DC 5V supply is given below.

Operation of Circuit: In above circuit, a transformer T takes 220V AC in its primary and steps down it into 12V AC in secondary. A bridge rectifier which is created with 4 diodes D1 – D4 takes this 12V AC in its input and converts it into 12V DC as its output. This output is not pure but pulsating DC which has ripple in its wave. The 2200µF, 35V capacitor is connected in parallel with output of bridge rectifier and acts as a shunt capacitance filter which removes the ripple from pulsating DC and makes it near to pure DC. The 7805 is a 3-terminal constant +5V regulator IC. It takes +12V between its pin no 1 and 2 as input and supplies constant +5V between pin no 3 and 2 as output. An indicator LED can be connected with 470Ω resistor between two points a’ and b’ as shown in above figure which indicates the output state of DC power supply either ON or OFF. We can get constant +5V supply between two points a’ and b’. N. B. Input voltage of regulator IC 7805 should be 25VVpin1≥7V.

Part List:

(i) Step down transformer 220V/12V……………. 1 No.
(ii) Diode 1N4007 ……………………………………… 4 No.
(iii Electrolytic capacitor 2200µF, 35V …………. 1 No.
(iv) Regulator IC 7805 ………………………………. 1 No.
(v) Resistor 470Ω, ¼ watt ……………………… 1 No.
(vi) LED ……………………………………………………. 1 No.
(vii) Connecting wire ………………………………… 1 Meter
(viii) Solder ………………………………………………….… 1 Meter
(ix) Vero board ………………………………….………. 1 Meter

 

Variable 1.2V~37V DC Power Supply

 

Schematic Diagram: A schematic diagram of variable DC 1.2V – 37V supply is given below.

Operation of Circuit: In above circuit a transformer T takes 220V AC in its primary and steps down it into 40V AC in secondary. A bridge rectifier which is created with 4 diodes D1 – D4 takes this 40V AC in its input and converts it into 40V DC as its output. This output is not pure but pulsating DC which has ripple in its wave. The 2200µF, 50V capacitor is connected in parallel with output of bridge rectifier and acts as a shunt capacitance filter which removes the ripple from pulsating DC and makes it near to pure DC. An indicator LED can be connected with 202kΩ resistor between two points filter capacitor as shown in figure which indicates the output state of DC power supply either ON or OFF. The LM317T is a 3-terminal variable 1.25V~37V DC regulator IC. It can take up to 40V with respect to GND into its pin no 3 as input and supplies variable Vout = 1.25V~37V with respect to GND through pin no 2 as output. Vout can be adjusted by changing the position of variable resistor R2. We can get variable 1.25V~37V supply between two points a’ and b’. N. B. Input of regulator IC LM317T should be 40VVpin3≥3V .

Part List:

(i) Step down transformer 220V/40V……………. 1 No.
(ii) Diode 1N4007 ……………………………… 4 No.
(iii) Electrolytic capacitor 2200µF, 50V………… 1 No.
(iv) Regulator IC LM317T………………………………. 1 No.
(v) Resistor 2.2kΩ, ¼ watt ……………………… 1 No.
(vi) Resistor 240Ω, ½ watt ……………………… 1 No.
(vii) POT 5kΩ ………………………………………..… 1 No.
(viii) LED ……………………………………………………. 1 No.
(ix) Connecting wire ……………………………….. 1 Meter
(x) Solder ………………………………………………….… 1 Meter
(xi) Vero board ……………………………………….…. 1 Meter

 

 

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